Lecture 19 - Community Ecology- Competition

What determines where a species lives?

- dispersal
- abiotic conditions: climate and nutrients
- species interactions: competition, predation, mutualism,

What are the different types of species interactions and their oversimplification?

- competition: bad for both species A and B
- predation: good for species A and bad for species B
- mutualism: good for both species A and B

What do ecologists and evolutionary biologists study?

ecologists - population dynamos and effects on community
- how species interact

evolutionary biologists - evolutionary dynamics
- adaptation, coevolution
how species interactions affect adaptations

What is INTRAspeific competition? What does conspecifics mean?

- competition among the same species for resources
- individuals of the same species

What is INTERspecfic competition? What does heterospecifics mean?

- competition among different species for resources

- individuals of different species

What is scramble/exploitative competition?

-depletion of shared resource
- individual consuming a resources, leading less for others

What is contest/interference competition?

direct interactions, battles over territory

What is an example of interference/contest competition?

invasive Argentine ants are superior competitors
- drive down populations of native species
- compete for space

What is an example of exploitative/scramble competition?

- two species don't interact directly
- one consumes resource, leaving less for another species

How can we model INTER specific competition?

- Lokta-Volterra equations for two species competing for resources

What is the Lotka-Volterra model for interspecific competition? How do we model it?

1. start with logistic model for population growth (intra)

dN/dr = rN(1-N/K)

2. rewrite the logistic model with subscripts to indicate species

dN1/dt = r1N1 (1-N1/K1)

3. add terms to show affect of species 2 on 1

dN1/dt = r1N1 (1-N1/K1 - a12N2/K1)

- models effect of completion one species has on species 1
- as more species 2, its going to slow population growth for species 1

What is the final Lotka-Volterra Model Equation? What do they mean?

dN1/dt = r1N1 (1-N1/K1 - a12N2/K1)

- a12 represents the per capita effect that species 2 has on species 1

dN2/dt = r2N2 (1-N2/K2 - a21N1/K2)

- a21 represents the per capita effect that species 1 has on species 2

What does the alpha term mean?

per capita effect on a on b

- competition coefficient

What does a12N2 do? Give an example?

converts individuals of species 2 into equivalent number of individuals of species 1

- squirrel eats more seeds than sparrow
- a is how many sparrows amounts of seeds a squirrel can eat

- sparrow eats less than squirrel
- a is how many squirrels worth of seeds a sparrow can eat

What are possible outcomes of LV competition? What does it depend on?

- species are able to coexist
- species 1 always wins (N1=K1, N2 = 0)
- species 2 always wins (N1=0), N2 = K2)
- depends on initial populations

What does coexistence require?

- intra competition be more stronger than inter competition
- outcomes depend on K value and a values

What does equilibrium mean?

population is not changing over time (dN/dt =0)
- community is at equilibrium if the same species are present as a year ago

What does stability mean?

- ability of system to return back to equilibrium after a disturbance
ex. hurricanes, wildfire

What does coexistence mean?

- occurs when two or more species have non-zero population sizes at equilibrium
- they persist in a community

What are principles of competitive exclusion?

- for two species to coexist, competition btw them must be weaker than competition within species

- two species can't compete too much or one will overpower the other

- complete competitors cannot exist

What leads to competitive exclusion?

limited resources, food, or space generate competition among individuals

What is niche partitioning? Hint: warblers (birds)

- exist by partitioning resources
- feed in different parts of this trees

What did Robert MacArthur experiment?

- measured how much time each species spent in different parts of the trees
- feed in different parts
- evidence that similar species coexist in communities but in diff niches
- don't violate the principle of competitive exclusion

What is character displacement? Hint: finches. What effect does this have on completion between species?

- trait evolution
- coexisting pieces evolve differences

- living separately they have overlapping beak sizes
- islands that have both, don't have overlapping beak sizes
- one has evolved smaller, one evolved larger

- reduces competition
- how competition selects organismal traits
- how competition for resources led to this trait adaption

What is the paradox of the plankton?

- principle of competitive exclusion is false for plankton
- plankton coexist but also compete fore the same resources
- phytoplankton need light, CO2, N, P, and micronutrients

What is the paradox of tropical rainforests?

- each species has distinct Niche
- something prevents competitive exclusion from driving species extinct

How do LV models relate to the real world?

- studied competition among protozoa
- saw stable coexistence and competitive exclusion

What was Gauses's experiment? What do these graphs show us?

- grew three different bacteria species
- placed first two tgt and saw competitive exclusion
- place other two together and saw stable coexistence

How are competitive effects manifested in nature?

- competitive exclusion is less likely to go to completion
- different outcomes in different environments

What is an example of testing competition experimentally? Hint: barnacles. What was the result of the experiment?

- upper zone had Chtamalus to thrive because of desiccation
- balanus can't toleration being out of water, risking desiccation
- lower zone had balanus by competing for space

What does competiton effect?

- affects which and how may species occur in an ecological community

- community composition : which
- species richness : how many

What is true about LV models and real communities?

- LV models are too simple
- communities are not at competitive equilibrium

How are real populations kept below carrying capacity?

because of weather, diease and predators

- conditions fluctuate and favour different species at diff times